Larvae of Florida Keys Ochlerotatus taeniorhynchus collected from No Name Key were colonized and evaluated against technical S-methoprene in laboratory beaker tests. Glassware was treated with a silanizing reagent before testing to prevent methoprene attachment to the glassware. The No Name Key strain was compared with a susceptible laboratory strain of Oc. taeniorhynchus. Five serial dilutions (0.0100, 0.0050, 0.0010, 0.0005, and 0.0001 microg/ml) and an untreated control were evaluated. Tests were conducted in water baths with a constant water temperature of 27+/-1 degrees C and 250 ml of 3 per thousand salt water. Twenty-five late 3rd-stage larvae were placed in each beaker. Bioassay samples were analyzed by probit analysis and the median lethal concentration (LC50), 90% lethal concentration (LC90), and 95% lethal concentration (LC95) values; confidence limits; chi2 value; slope; and standard error were determined. The Florida Keys No Name Key strain exhibited no significant differences at the LC50, LC90, and LC95 levels from the laboratory strain in these studies.